Bottlehead Forum
Bottlehead Kits => Eros Phono => Topic started by: dehringer on December 22, 2022, 05:57:21 AM
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I have some high voltages on one side of the CS4 board in my Eros 2 build. All earlier tests in the build have passed.
IA: 217
IB: 215
OA: 144
OB: 158
OC: 141
OD: 107
OkA: 139
OkB: 102
OkC: 11.8
OkD: 1.8
I have gone back to check the solder joints on the board (although I could be missing a bad joint(s)).
Do you have recommendations on what to focus in on? I’ve attached a few pictures.
Thanks for the help!
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Something like the Q2C center leg not getting adequately heated could cause something like this.
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Yes, after looking closer, the middle leg of Q2C didn’t have the solder flowing fully through. I think I have resolved this but the voltages are measuring the same.
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I would reheat the rest of the resistor and transistor joints on that front PC board. The LEDs generally solder easily and don't require extra effort.
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I’ve reheated all the joints 3 times and continue to get the same measurements. :-\ I could only assume I need to worry about the joints on the side of the board with the measurement issues?
I might need to take a break and come back with a fresh set of eyes unless you recommend anything else.
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A miswire or a problematic solder joint on that 9 pin socket could also cause some problems.
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The lead on the 0 ohm resistor going through A3 was touching A4. I resolved that and it brought OkC down a little bit to 5.2 volts but others didn’t change. Would this issue have caused any damage to the tube?
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That could possibly damage the 2N2222 on that side of the small PC board.
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Would a damaged 2N2222 potentially be the cause of the high voltages I’m measuring? Or should I continue to try to track down potential a bad solder joint or mis-wire?
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If you are not sure you should probably test the 2n2222 to see if it is shorted.
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I finally got a chance after the holidays to come back to this build. I removed the 2n2222 transistor and it tested ok. I also removed and tested all the other transistors on the same side of the board and I believe they all tested ok.
I tried reflowing all the joints on that side of the board again. I also reflowed all the point-to-point joints as well. I’m still getting high voltages. Current readings:
IA: 217
IB: 215
OA: 144
OB: 158
OC: 141
OD: 107
OkA: 140
OkB: 102
OkC: 4.5
OkD: 1.8
Do you have any recommendations on additional troubleshooting steps?
Thanks!!
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If you have the equipment to easily swap the 2N2222 transistors, I would try that.
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I don’t have a component readily available but I can get one and give that a try!
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Thanks to being able to borrow a 2N2222 from a new kit that arrived today 8) , I was able to try this out faster than anticipated.
Unfortunately, with the new 2N2222 the voltages remain the same. :-\ Could any of the other transistors have been damaged? None of them tested as being shorted.
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Generally high voltages on the output of the C4S can be attributed to the center leg of Q2 not being sufficiently soldered.
In your case, the voltage isn't so high that I believe this is the problem. This is more likely to be something like a swapped resistor or backwards component throwing things off. I cannot ever remember building a C4S board and just randomly having a defective transistor (and I've been somewhat regularly doing that for 23 years).
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With regard to the transistor question, I wasn’t sure if the lead on the 0 ohm resistor going through A3 touching A4, that I mentioned above and led to trying to swap the 2N2222, could have impacted any of the other transistors.
I believe I’ve verified all the resistors on the CS4 board are in the correct place and the components on the board are correctly oriented.
Would any of the resistors off the CS4 board affect the specific voltages I’m having issues with? (I’m learning the importance of resistor orientation for the non-striped resistors when you place it so that you can see the part numbers so you don’t have to remove the resistor from circuit to test it with a multi-meter to know what it is….)
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You can measure the R1 resistors while they are mounted to the board.
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The R1 and all other resistors on the board are correctly placed.
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Having repaired a great number of these kits, most of my repair efforts are spent at fixing flaky solder joints and occasionally a backwards part or a miswire.
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I don’t doubt at all that it is likely one of those issues. I have either reinspected, reheated, removed and resoldered everything on the side of the CS4 board in question at least 10 times. So I think the board is ok. Are there any other areas of the circuit I should be focusing in on given the specific voltage issues?
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What are the Kreg voltages on the back board?
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The Kreg voltage on the A side is 6.6 and on the B side is 6.3.
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That tells you that each half of the front board is (very likely at least) attempting to deliver the appropriate amount of current.
I would be very suspicious that the 47K 2W resistor on that side of the front C4S board isn't well soldered in.
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To start from a semi-clean slat, I desoldered, removed, and resoldered the 47k resistor on that side of the CS4 board. I’m still seeing the same voltages. :-[ ((scratching head))
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Could I see some pictures of your D socket wiring?
Your 6922 plate and cathode are about at the same voltage, which is really the root of the issue. This could happen if those pins are somehow shorted together on the 9 pin socket, then the rest of the circuit would respond by trying to correct that issue.
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Sure thing. I’ve attached pictures of the D socket from a few different angles, trying to get a decent view under the board above it. Let me know if these are sufficient.
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Additional picture
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Let's also see the C socket as well.
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Here is the C socket.
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If you pull out the 6922, then measure the DC resistance between pins 1 and 3 on that socket, what do you get? How about between pins 6 and 8?
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With the 6922 tube out,
Between C1 and C3: 73.6k
Between C6 and C8: 73.7k
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How about C1 to C2, C2 and C3, C6 to C7, C7 to C8?
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C1-C2: 121.8k
C2-C3: 102k
C6-C7: 121.8k
C7-C8: 102k
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Can you run the amp with just the 12AU7 (no 6922, and no EF86s), then let me know what the OA and OB voltages are on the front C4S board? OKA and OKB voltages would also be of interest.
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Sure thing.
With only the 12AU7:
OA: 214.8 V
OB: 213.6 V
OKA: 0.2 mV
OKB 0.1 mV
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I would attempt to procure a different 6922 or 6DJ8 and try that in the C socket. When your amp is running, it's acting like there's a short between plate and cathode on that side of the 6922, which could be from debris in the socket, but that would appear as a DC resistance difference between sides on the socket and would be persistent with the tube out of the socket.
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Ok, sounds like a plan. I’ll do that and when it arrives report back. Thanks Paul!
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I tried a different 6922 in the C socket and unfortunately did not resolve the high voltages. Updated voltages:
IA: 217
IB: 230
OA: 145
OB: 160
OC: 140
OD: 98
OkA: 139
OkB: 100
OkC: 4.7
OkD: 1.6
Are there any other things I should try?
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Perhaps PJ has some ideas about why this might be happening.
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I'll take a closer look, but it may take a few days - PB revised the layout and the PC board to make the Eros II much easier to assemble. It's a great improvement, but I'm not yet intimately familiar with the new board.
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IA: 217
6DJ8 plate A: 145
EF86 plate C: 140
EF86 screen/DJ8 cathode A: 139
EF86 cathode C: 4.7
This is the voltage set on the offending side.
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4.7v on OkC tells us that the EF86 is cut off - the 2N2222 bias servo is not conducting.
102k ohms between C2 and C3 tells us that the 174-ohm resistor is connected at least.
But the 174-ohm resistor may be shorted, or the 2N2222 base may not be connected to that resistor. Check the voltage across that resistor - it should be around 0.6v. If it's closer to zero, the resistor is shorted. If it's closer to 0.8, the transistor may not be connected at the base.
Or the 2N2222 collector may not be connected to the EF86 cathode (A3). The collector should also be connected to one end of the 0.1uF Z5U on the PC board, and to the + end of the cathode capacitor, which is (I think) the 10000uF/6v cap (shown on the circuit diagram as 2200uF/4v as was originally used (I'm not certain of that change). Check those capacitor voltages to identify where the break may be.
I notice that the original measurement of OkC was 11.8v, which could have damaged the 10000uF cap. There's probably not enough current available to damage it severely, but you might want to replace it after the real problem is corrected, just to be sure.
That's my first shot at identifying the problem, anyhow!